Overweight and Obesity Epidemic in America – Part VIII: Dieting Is Not An Effective and Healthy Treatment For Overweight and Obesity

Michael G. Garko, Ph.D.

Host – Let’s Talk Nutrition

Introduction

Dieting does not work in the treatment of overweight and obesity.[1] Specifically, dieting is not a successful, scientifically and clinically proven method of achieving sustained, long-term weight loss. That is the bad news. The worse news is that not only does dieting hinder the achievement of successful weight loss or is otherwise counterproductive but that it most often leads to weight cycling (i.e., repeated losing and regaining of weight), which has been shown to put the health of dieters in further jeopardy.

Thus, dieting can be and is too frequently a harmful method of weight loss resulting in only nominal, short-term success, with any of its potential benefits being outweighed (no pun intended) by serious, adverse health effects. Mann et al. (2007) state it this way: “The benefits of dieting are simply too small and the potential harms of dieting are too large for it to be recommended as a safe and effective treatment for obesity”(Mann et al., 2007, p. 230).

The May, 2011, issue of Healthful Hints takes a look at dieting in terms of what the scientific literature reveals about its efficacy to achieve sustained, long-term weight loss and health and, consequently, its usefulness and safety as a treatment for overweight and obesity. The focus is put primarily on long-term and not short-term weight loss because while short-term weight loss may be of some temporary help for those who are overweight, it is long-term weight loss that addresses more directly the greater challenge of overcoming overweight and obesity and helping to resolve the overweight and obesity epidemic in America[2]. To date, Mann et al. (2007) provide one of the best literature reviews and assessments of the efficacy of dieting and the long-term outcomes of calorie-restricting diets and whether or not these types of diets are an effective treatment for obesity. Rather than reinventing the wheel, my discussion on dieting and whether or not it is an effective and healthy treatment for overweight and obesity draws in large measure from the cogent and insightful literature review of Mann et al. (2007).

What Is Known About The Long-Term Efficacy Of Dieting

Basically, there are at least three conclusions which can be reached about the effectiveness of dieting for long-term loss of weight. First, weight-loss diets result generally in a short-term reduction in weight, with an average loss being between 5% – 10% of dieters’ original weight. Second, any loss of weight which dieters are able to achieve is temporary and not sustained over time. Third, when dieters are followed as part of a weight-loss program, studies indicate that as more time passes between the conclusion of a diet and follow-up the more weight that is regained. In that regard, there is evidence stemming from studies with the longest follow-up periods (i.e., 4-5 year follow-up) suggesting that weight regain would most likely continue to increase with a longer follow-up (See Mann et al., 2007).

Research Designs Used To Measure Effectiveness of Dieting

In their review of the literature of the long-term outcomes (i.e., effectiveness) of calorie-restricting diets, Mann et al. (2007) examined randomized, controlled studies in which participants were randomly assigned to a diet group or nondiet group (i.e., control group) and followed long-term. This is an effective research design in that causal conclusions can be made about the long-term effectiveness of dieting due to randomization and comparison between dieters and nondieters.

Mann et al. (2007) also included in their review observational studies, which used a no control group, dieters-only design, in which participants in a structured weight loss program were followed-up on 2-5 years upon conclusion of their diet. Not having a control group of non-dieting participants does not allow for a comparison between dieters and nondieters, which in turn does not allow for causal conclusions to be reached about the effectiveness of dieting in long-term weight loss.

Finally, Mann et al. (2007) analyzed observational studies using a cohort prospective, nonrandomized design in which the researchers had no control over assignment into the nondieters group and the weight and diet statuses of dieters and nondieters (i.e., control group) in the cohort were measured at baseline and their weight measured at follow-up points. A cohort is a group of individuals who share many characteristics in common but are different in a particular feature such as being overweight or obese. Although these studies used a control group of nondieters, not randomly assigning participants into a dieters or nondieters group does not permit causal conclusions about the long-term effectiveness of the weight-loss program.

It is important to consider the types of research designs used in studies intended to measure the effectiveness of calorie-restricting diets because the type of design used determines what sort of conclusions can be reached and whether comparisons can be made between dieters and nondieters. Without randomization and a control group conclusions of a causal nature cannot be made. Within the context of trying to determine the efficacy of dieting, both are necessary conditions to make statements about whether or not a particular weight-loss program caused long-term weight loss. Causation is the research gold-standard in science. Nonrandomized and no-control group designs only allow for conclusions of a correlational nature to be made. Correlation is a necessary condition for causation and is, thus, a step down from causation. Knowing what causes something to happen and knowing how one thing is associated with another are entirely two different levels of knowing.

Notwithstanding differences in their research design, all of the studies included in Mann et al.’s (2007) review involved long-term follow-up of dieters and how successful they were in losing weight in terms of how much weight they lost and whether or not their weight-loss was sustained long-term. As it was pointed out earlier, if dieting is to be considered an effective strategy in addressing the overweight and obesity epidemic in America, then it needs to be effective in long-term weight loss, otherwise overweight and obese individuals remain overweight or obese and the epidemic continues.

How Much Weight Is Lost

All of the studies included within the three research designs presented below employed a long-term follow-up from two to five years.

Randomized Controlled Studies

There are very few randomized, controlled studies (i.e., studies with randomized assignment of participants to a diet group or wait-list/nondieters control group) with a long-term follow-up period of at least two years to compare how much sustained weight loss there is between dieters and nondieters. Nevertheless, the few studies that do exist (most of which are not formal diet studies) show that dieters do not do any better at sustained weight loss than nondieters. Mann et al. (2007) commented that “there is not strong evidence for the efficacy of diets in leading to long-term weight loss” (p. 223). Some studies show no statistically significant differences between dieters and nondieters in the amount of weight loss maintained. In those studies where statistically significant differences were found, the extent of the weight loss maintained was rather small. Mann et al. (2007) reported the following regarding the amount of weight loss maintained by dieters and nondieters:

The amount of weight loss maintained in the diet conditions of these studies averaged 1.1-kg (2.4 lb), ranging from a 4.7-kg (10.4 lb) loss to a 1.6-kg (3.5 lb) gain. Participants in the control groups averaged weight gains of 0.6-kg (1.3 lb); ranging from losses of 0.9-kg (1.9 lb) to gains of up to 1.8-kg [3.9 lb]). The most positive conclusion is that dieting slows the slight weight gain that occurs with age among the average nondieters, and even this slight weight gain was not seen in all of the no-diet control groups. It is hard to call these obesity treatments effective when participants maintain such a small weight loss. Clearly, these participants remain obese” (p. 223).

Observational Studies – No Control Group

Mann et al. (2007) reviewed 14 studies in which participants were followed for at least four years upon conclusion of a diet. The average weight loss in these studies was 14 kg (30.8 lb). At the time of long-term follow-up, dieters regained all but 3 kg (6.6 lb.). In eight of the studies, dieters weighed more at follow-up than prior to going on a diet. The rate of weight regain was 41% with the rate of weight regained above original weight at start of diet ranging from 29%-64%. Fifty percent of the dieters in these studies weighed more than 5 kg (11 lb) above their starting weight five years subsequent to the conclusion of their diet programs. It is not uncommon for investigators to not report the amount of weight regained above and beyond the starting weight of dieters.

Mann et al. (2007) contend that the effectiveness of dieting is most likely even more bleak than the findings mentioned above. They give four methodological reasons why this could be the case: 1. The response rate for follow-up is low, especially for studies with long-term follow-up; 2. many dieters self-report their weight by telephone or mail; 3. most studies suffer from confounding the effects of dieting with exercise; and 4. a large number of dieters have gone on other diets since the conclusion of the diet which was being studied.

Observational Studies – Non-randomized Cohort Prospective Studies

In cohort prospective studies using a non-randomized design participants’ weight and diet statuses are measured at baseline and at follow-up. Although they are not randomly assigned, comparisons can be made between dieters and nondieters. Of the ten studies Mann et al. (2007) reviewed, only one reported weight loss. Two reported no correlation between dieting and weight change. Seven reported dieting leading to weight gain.

These seven studies are of special interest because they suggest that dieting may be more harmful than helpful in that “dieting history is related to risk for future weight gain” (Mann et al., 2007, p. 220). As it turns out, studies suggest that dieting is a good predictor of future weight gain and obesity. Furthermore, research on the effectiveness dieting suggests that more weight is gained by dieting and not dieting.

Conclusion

According to the National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention (CDC), the National Health and Nutrition Examination Survey (NHANES) revealed that in 2007-2008, when adjusting for age, an estimated 34.2% of American adults 20 years of age and older were overweight, while 33.8% were obese (Ogden & Carroll, 2010). The overall prevalence estimates for overweightand obesity when combined for adults 20 years of age and older (BMI 25) is a stunning 68.0%(Ogden & Carroll, 2010). Another way to think about the overweight and obesity epidemic is that less than a third of adults (i.e., 31.6%) in the United States are at a healthy weight. Of the total percentage of healthy weight adults, 36.5% and 26.6% are women and men, respectively (see National Institute of Diabetes and Digestive and Kidney Diseases, 2010).

These bulging statistics on overweight and obesity help explain why a large percentage of the U.S. population is obsessed with losing weight. In 2004, the Calorie Control Council’s survey on Americans’ dieting habits and attitudes about weight loss revealed that 33% (71 million) of U.S. adults were on a diet. This reflected a sizeable increase from 2000 when 24% of Americans were on a diet.

With so many Americans being obese or overweight and a substantial number dieting, it is no wonder that there is always a steady crop of either new or recycled fad diets. Just as one diet moves out of vogue another one emerges to take its place. If they did not possess the potential to be so harmful to the health of those who try them, then health care professionals and organizations would not be as concerned about them as they are. The American Heart Association (AHA) was so concerned that it actually declared war on fad diets. They did so “to inform the public about misleading weight-loss claims.” For the AHA, “many of the fad diets in circulation such as the infamous cabbage soup diet have the potential to undermine people’s health, cause physical discomfort and lead to disappointment when dieters regain their weight not long after they lose it.

The studies included in the discussion above on the efficacy of dieting reveal that dieters have difficulty in maintaining weight-loss in the long-term and do not glean any meaningful health benefits from dieting. Not only do they tend to regain more weight than they lost, dieters also put their health in jeopardy with weight cycling. Therefore, dieting is wishful thinking and willful action leading more often than not to weight-loss failure.

While there is only minimal success associated with dieting in terms of losing weight and keeping it off long-term, it does not deter dieters from trying one or another fad diet or weight loss program, often with the knowledge that dieting does not work and can be deleterious to one’s health. Dieting is sort like entering a Las Vegas casino with the ill-fated belief that the house can be beaten, when the odds of the losing are far greater than winning. Once in awhile someone may beat the house (similar to a dieter losing weight). However, in the long run and for the majority of gamblers (and dieters alike), the odds of gamblers continuing to win the pot (and dieters losing their pot) with any degree of sustained success are abysmal.

It is clear from the research that dieting is not an effective and healthy treatment for overweight and obesity. If this is so, then what is? In upcoming issues of Healthful Hints specific dietary and lifestyle principles and strategies will be presented to help those individuals who are overweight or obese increase their chances of losing weight and keeping it off.

[1]Dieting is defined specifically as the behavior of restricting the consumption of calories for the purpose of losing weight.

[2]Overweight is defined as an excessive amount of body weight, which can be constituted of muscle tissue, bone, adipose or fat tissue and water, while the term “obesity” refers to an excessive amount of adipose or fat tissue (see National Institute of Diabetes and Digestive and Kidney Diseases, 2010). Body Mass Index (BMI) is used to measure the amount of body fat/adipose tissue based on a person’s height and weight. Specifically, BMI is expressed as a person’s weight in kilograms divided by height in meters squared (kg/m2). Individuals with a BMI of 25.0-29.9 are classified as being overweight, while those with a BMI of 30 or more are classified as obese and those with a BMI more than or equal to 40.0 are classified as extremely obese (see Ogden and Carroll, 2010).